The aim of this study is to evaluate the performance of a double labelling method using isotope and methylene blue dye injection to localize precisely Sentinel Lymph Node (SLN) in a series of 100 patients with infiltrative breast cancer justifying SLN excision. Method and patients: SLN excision will be performed on 100 patients treated for infiltrative breast cancer. After preoperative methylene blue dye injection and lymphoscintigraphy, individual localization of the radioactive and stained nodes will be performed. After the surgery, SLN will be submitted to serial analysis and immunohistochemistry. A comparison of the two methods and an economical evaluation of the complete procedure will be performed.